Method of forming stressed concrete

ABSTRACT

A method of forming stressed concrete articles including post tensioning of a stressing tendon and utilizing an anchorage assembly including an anchor having a hollow housing and means therein for engaging a stressing tendon passing therethrough. The assembly includes a hollow member removalby attached to the anchor housing and to the concrete formwork and fixing the relative position of the anchor housing to the formwork. The member surrounds the tendon between the anchor housing and the formwork and is adapted and arranged to be detached from the anchor housing after the concrete has set. A cavity forming spacer is provided which surrounds the member and is disposed between and seals against the anchor housing and the formwork to form a cavity in the concrete. The spacer is adapted and arranged to be removed from around the member after the concrete has set.

Sept. 3, 1974, H. J. w. EDWARDS 3,833,706v

METHOD OF FORMING STRESSED CONCRETE Original Filed Aug. 27, 1968 2Sheets-Sheet l -nj i? W6 l Y FIGA I 46.', 42

72 Fl G., 5

4 l INVENTOR. yg yf 94 2f /f/y J//ff'dwmff Fler! 42 BY l 44 ,26 M 64 GMMA TTQRNEY 542933, 1974 HJ. w. EDWARDS 3,833,706

METHOD OF FORMING STRESSED CONCRETE Original Filed Aug. 27, 1968 2SheetsSheet 2 fsa M4 126 INVENTOR 1,34 /fa/y d. Kiowa/'afs U.s. Cl..gt4-2s 10 claims .ABSTRACT vOF THE DISCLOSURE .-A methodiof formingstressed concrete articles including post tensioning of a stressingtendon and utilizing an anchorage assembly including an anchor having ahollow housing and means therein for engaging a stressing tendon passingtherethrough.-The assembly includes a hollow member Vremovably attachedto the anchor housing and to the concrete formwork and fixing therelative position o f the anchor housing to the formwork. The membersurrounds the tendon between the anchor housing and the formwork and isadapted and arranged to be detached from theanchor housing after theconcrete has set. A cavity; forming spacer is provided which surroundsthe member and is disposed between and seals against the anchor housingyand the formwork to form a cavity in the concrete. The spacer isadapted and arranged to be removed from around the member after theconcrete has set.

CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION Fieldof the invention This invention relates to the post-tensioning ofconcrete structures by means of wire or strand cables. In particularthis invention concerns an anchorage device or assemblyand partsthereoffor use in anchoring a cable or cables in a concrete structure.-In greater detail the invention -pertains to anchorages for concretestressing tendons, particularly to anchorage assemblies for use in thetensioning of such tendons positioned within concrete structures afterthe concrete has set or cured.

For Amany years Ymild, low strength steel reinforcing was simplyimbedded in ordinary concrete and the result Iwas an improvement in thestrength of the concrete and someresistance to cracking and otherfailures was btained. Later there was an attempt to place thisreinforcement under tension so that it would have a compression effectuponthe concrete. This slightly improved the construction although thesuccess of this effort was not great becausepthose who did it did notappreciate the fact that concrete -would flow slightly under pressurethus that tension .on the reinforcement would be reduced practicallyback to. zero. Also under tension, the reinforcement itself wouldv.suffer from s omepermanent elongation that would add tothis reductionof the tension. Accordingly, the tensioning ofthe reinforcementv was notgenerally considered tozbe of great importance until recently when someof the factorsintiuencingthe effectiveness of reinforcement becamebetter known and it was found that if steel wire having a very hightensile strength was used and placed under aqvery high tension, thenalthough a part of the tensiOll. Waslost by-plastic flow and shrinkagein the concrete and permanent elongation or creep in the wire,nevertheless *sufficient tension would remain in the wire and,suticientcompression would result on the concrete to cause amajor increase -inthe load-carrying ca- Patented Sept. 3, 1974 pacity of the concrete anda major increase in the resistance of the concrete to cracking and thelike. This represented such a complete departure from previously Iknownfacts to present completely new concept in reinforced concrete and hencethis high tension wire reinforcing of concrete was probably consideredto furnish a cornpletely new and different approach to reinforcedconcrete construction. At the time that the possibility of usinghightension wire reinforcement came into being a general idea oftensioned reinforcement had long been known and considered of relativelylittle value. The discovery that high-tensioned wire reinforcement couldproduce far stronger and more durable structures than had ever beforebeen known was a discovery that revolutionized the manufacture ofreinforced concrete structures.

Description of the prior art Anchors or anchorage assemblies for use inthe posttensioning of stressing tendons within concrete structures havebeen previously devised, such prior art devices are generally disclosedin U.S. Pat. No. 3,293,811. Applicants invention of an improvedanchorage assembly disclosed herein is an improvement over such priorart anchorage devices or assemblies, as shown for example in the abovementioned patent.

SUMMARY OF THE INVENTION Therefore it is an object of the invention toprovide an improved anchorage assembly for concrete stressing tendons ofthe type which are cast in place in such a manner that they may betensioned after the concrete has set or `been cured.

Another object of this invention is to provide an improved anchorageassembly for concrete stressing tendons in which there is utilized asingle piece, wedge receiving and constraining plate anchor housing.

Still another object of the subject invention is to provide an anchorageassembly for concrete stressing tendons which includes a cavity formingspacer initially held in being engagement with the wedge receivinganchor housing and in being engagement with the concrete formwork whenanchorage is secured to the formwork such as to provide a groutreceiving cavity, the spacer forming an effective seal with the wedgereceiving anchor housing to exclude concrete therefrom Where theconcrete is being poured and cured.

Yet another object of the instant invention is to provide means wherebya tendon anchoring housing is imbedded in the concrete at the time theconcrete is poured and by which means the anchor housing is attached tothe formwork, and after the concrete has set the means permitting theformwork to be released from the anchor housing.

A further object of this invention is to provide an improved anchorageassembly for concrete stressing tendons wherein portions of theanchorage assembly may be salvaged and later re-used.

Yet a further object of the invention is to provide an anchorageassembly which will permit the anchor housing thereof to be left in theconcrete and which anchor housing when left in the concrete will notproduce an unsightly appearance.

In general these and other objects are attained byproviding an anchorageassembly including an anchor having a hollow housing and means thereinfor engaging a stressing tendon passing therethrough. The anchorageassembly includes a member removably attached to said housing and to theformwork, this member fixing the relat tive position of the anchorhousingy with respect to the formwork. The member is additionallyadapted and ar- The concrete objects produced in accordance with theapparatus of this invention may be of any desired shape ibut aregenerally beams, columns, channels, slabs or other like structuralmembers. In accordance with this invention, the concrete objects arecomprised of three essential parts, namely, the concrete itself,reinforcing members or tendons and the end anchorages that transfer theload of the reinforcing tendons to the concrete.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features which are believedto be characteristie of this invention are set forth with particularityin the appended claims. The invention itself, however, both as to itsorganization and method of operation, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings, inwhich:

FIG. 1 is a side elevational view, portions thereof being incross-section, of the improved anchorage assembly of this invention;

FIG. 2 is a left-hand end view taken along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a side view of the anchor housing shown in FIGS. 2 and 3;

FIG. 5 is a prospective view of the wedges used in the assembly of FIG.1;

FIG. 6 is a prospective view of the reusable bayonet fitting used in theassembly of FIG.V l;

FIG. 7 is a transverse-sectional View taken along line 7 7 of FIG. 3;

FIG. S is a cross-sectional view showing a second embodiment of theanchorage assembly of the invention;

FIG. 9 is a cross-sectional View taken along line 9 9 of FIG. 8;

FIG. l is a cross-sectional View taken along line 10-10 of FIG. 8; and

FIG. 1l is a top plan view of the reusable bayonet fitting used in theassembly of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to thedrawings, and in particular FIG. l thereof, the anchor or anchorageassembly 10 of this invention is depicted therein retaining anappropriate strand or tendon 12 to be used in the construction of aconcrete beam, column, slab or the like. Cable or tendon 12 when usedwith the anchorage assembly of this invention in its intendedapplication is often of the non-bonded type. This type of cable(non-bonded) comprises the normal prestressing cable which beforedelivery to the site is pre-cut and coated with a special protection andlubricating compound which guards against corrosion and minimizesfriction during the stressing operation. The thus coated cable iswrapped in a special heavy duty reinforcing paper 14, as in FIG. 8, or aplastic sleeve or sheathing 16 is fitted over the entire length of thestand as in FIG. 1. In both cases the strand is free to move -within thecovering. When the cable arrives at the site it is simply laid out inposition and appropriate anchorage assemblies, such as at 10, arelocated on the ends thereof interiorly of the formwork or shuttering 18.After this the concrete is placed within the form with the anchorassembly 10 being recessed therein. When the concrete has set the tendonis then stressed by jacks which bear against the back of the anchorhousing.

Assembly 10 generally includes a tendon anchor or housing 20, see inparticular FIGS. 2 through 4; grips or teethed Wedges 22, see inparticular FIG. a recess or -pocket former or spacer 24 for recessinganchor 20 into the concrete; and a releasable bayonet tting or member26, see in particular FIG. 6, for maintaining the assembly in assembledform and when employed in combination with a nut 28 maintaining thecomplete and assembled asassavms Cil - r i sembly -rmly in position withrespect to the shuttering or formwork 18 at any desired locationthereon. The assembly is positioned on the formwork 18 at the desiredlocation by means of a hole or opening 30 extending therethrough thebayonet iitting 26 of the assembly vbeing positioned therethrough andsecuredby means of 'nutf28 being tightened on a threaded portion '32 ofbayonet suing 26. l' Y v The anchor or anchor housing 20 Aof anchorassembly 10 includes a forward end portion 31 having outwardly extendinglip 33, a rearward end portion 35, and a conical-shaped bore or hollowpassageway 34.extending theree through and through whichstrand Yortendon 12 passes. Bore or hollow 34 is provided with an .enlargedforward portion or passageway 36 having a forwardly'facing shoulder 38against which sheathing 16 abuts whereby the' same bunches up withinenlarged portion 36 to prevent the con-'-` crete from enteringinternally into the anchor assembly from this its forward end portion31. Bore or hollow-34'y is further enlarged by cavity 40 adjacent therearward end portion 35' of anchor 20 to form a rearwardlyfacingshoulder 42, against which the forward end portion 44 of releasablebayonet fitting abuts.'Anchor 20 further includes a rib or flange member46 of a generally rectangular shape having roundedcorners and positionedgen erally perpendicular to the axis of conical bore 34. Rib' or flange46 distributes the stressing forces into the con-vv crete and thusreduces the stress intensities in the anchor# age zone. Member 46additionally provides a safety factor in the fact that any badcompaction of the concrete in' the region of the face or forward endportion 31 of anchor 20 has less effect than would be the case if anchorhous" ing 20 were not provided with this flange or rib 46. Body portion20 further includes agenerally rectangular shaped flange 48 extendingoutward therefrom and positioned generally adjacent the'rearward endportion 35' thereof.v Flange member 48 distributes the stressing forcesinto the concrete which reduces the stress intensities in the anchoragezone. Flange member 48 is provided with a slotted opening 50 in its topportionA extending downward from its upper edge and a slotted opening 52in its bottom portion extending upward from its lower edge, see inparticular FIGS. 2 and 3. Slots 50 and 52`ar'e provided such that anchor20 may be secured tothe shuttering or framework 18 by means of nails(not shown) if so desired, ex?

tending through slots50 and 52 and into the formwork 18. Casing oranchor housing 20 is'further provided'with a pair of reinforcing ribs ormembers r54'and` 56 extiende'VL ing from adjacent the rearward endportion 35 and adja-A" cent opening or cavity 40 upward to the upperouter edge of flange or plate member 48. In like manner, a second edgeof flange member 48.y

Wedges or jaws 22, see in particular 'FIGS '5f' have a conical shapedouter surface to generally conform to the conical configuration ofpassagewayor hollow 34' within anchor housing 20. Wedges 22 are provided'withi teeth or serrations 62 extending laterally round their inn'eropening or passageway 64 to grip and bite strand 12 pass-jingtherethrough, as depicted in FIG. 1. Jaws orwedgesK 22 are split andinclude a lleft' 66 andV right' 68'mernber or portion to tit aroundstrand 12 and generally' conform thereto as the jaws 22 are pulledforward 'within bore 34'.l Further, each of the jaw or wedge sections orportions 66"; and 68 are slit or provided with slotted" openings,vv re`spectively at 70 and 72 adjacent their mid portidrisjivhei j by theupper and lower portions'of eachwedge section" 66 and 68 may movevtowardeach 'otherto generally -con- 'passing' theret'hrough,A l

form to and better grasp' tendon 12 see also FIG. 3; l

ing a central bore or passageway: "74 vextendingtherethrough, with anenlarged forward end" portion "76 to per# mit bayonet fitting 26 toextend therethrough and to generally accommodate the same. Forward endportion 78 of lcavity forming spacer 24 abuts rearward end portion 35 ofanchor 20 to generally seal therewith to exclude the Vcement or groutfrom entering the anchorage assembly at this point. `In addition,rearward end portion 80 of recess former or spacer 24 abuts andgenerally seals with the forward edge of formwork 18 to prevent thecement from gaining access to the interior of the anchorage assemblyat'this particular location.

" Detachable and releasable bayonet fitting or hollow member 26 includesa circular elongated portion 82, a threaded outer end portion 32 and anenlarged circular forward portion 84 connected to portion 82 by atransition portion 86. Elongated portion 82 extends through opening 30within formwork 18 and through passageway or opening 74 within pocket orrecess former 24. Enlarged forward portion 84 of the bayonet fitting ispositionable within the enlarged rearward portion cavity `40 of thecasing or anchor housing 20 outwardly of the wedges or jaws 22 such asto not interfere with the operation of the same. The forward end portion44 of bayonet fitting 26 which abuts rearwardly facing shoulder 42 ofanchor 20 is provided with a pair 88 and 90 of flange members orshoulders (see FIGS. 3 and 7) which respectively fits behind and engagea pair of lips or shoulders 92 and 94 provided on anchor housing 20adjacent its rearward end portion 35 and extending inward of enlargedopening or cavity 40.

rUpon proper positioning of the forward end portion 44 of bayonetfitting 26 within cavity `40 of anchor 20 and rotation or pivoting ofthe fitting such that -ffange members 88 and 90 become engaged behindlips 92 and 94, the fitting 26 becomes releasably aixed or secured toanchor 20. The pocket or recess former 24 is then positioned overbayonet fitting 26 with enlarged forward portion 84 thereof fittingwithin the enlarged forward portion 76 of pocket former 24. Next thethreaded portion 32 of elongated portion 82 of fitting 26 is positionedthrough opening 30 within the formwork 18, and the nut 28 is threaded onportion 32 of bayonet fitting 26. Transition portion 86 of bayonetfitting 26 prevents jaws or wedges 22 from coming out of their properposition within bore or hollow 34 of the anchor housing 20. Nut 28 istightened on threaded portion 32 to pull bayonet fitting 26 throughformwork 18 causing the attached anchor 20 to tighten against pocketformer 24 thereby forming a seal between pocket former 24 and formwork18, and between pocket former 24 and anchor 20 to prevent cement fromentering the anchorage assembly 10 at these points of adjoinment. Nextthe concrete is poured and placed within the formwork or shuttering.After the concrete has set, nut 28, formwork 18, pocket former 24 andbayonet fitting 26 are removed to afford access to the back of anchorbody 20 and wedges or jaws 22 positioned therein, which are now recessedwithin the set concrete. The tendon may now be stressed by jacks whichbear against the back of anchor housing 20, and jaws 22 may be tappedhome to firmly and snugly grip the stressed strand 12. After stressingtendon-12, the opening in the concrete which was formed by the recess orcavity forming spacer 24 canY be grouted-in if so desired.

Withdetailed reference to FIGS. 8 through l1 now, a second embodiment ofthe anchorage assembly 100 is depicted therein retaining strand ortendon 12, having been. wrapped with heavy duty reinforcing paper 14, tobe used in the construction of a concrete beam, column, slab or thelike. Assembly 100 generally includes an anchor housing or casing 20',identical to that seen in FIG. 1 grips or teethed wedges 22', identicalto those shown in FIG. 5, a recess or pocket former 102 for recessingcasing or anchor housing 20 -into the concrete, a releasable anddetachable bayonet fitting 104, see in particular FIG. 1l, and a splitnut 106 for maintaining the assemblyfirmly in position with respectto kshuttering or formwork 18. -v

'Casing or anchor housing 20fof anchorage'assembly includes a forwardend portionl', a rearwardl end -portion 35,' and a conicalI shaped boreyor hollow 34' extending therebetween, through .which tendon 12 passi es.Bore 34' includes an enlarged forward portion or passageway 36 and anenlarged rearward portion orcavity 40. Anchorhousing 20 furtherincludesl a flange-like member "46' which aids in distributing andstressing forces into the concrete to thereby reduce the stressintensities in the anchorage zone, and provides a safety factor in thatany bad compaction of the concrete in the region of the forward endportion 31 of anchor 20' has less effect than would the same if theanchor housing were not provided with this fiange member 46. Anchorhousing 20' further includes a pair 92 and 94' of lips or shouldersadjacent rearward end portion 35 extending inward of enlarged rearwardopening or cavity 40', behind which bayonet fitting 104 is engageable,as will be explained more fully hereinbelow.

In the embodiment of the strand anchor assembly shown in FIGS. 8 through11, a grout or cement ex'truder or bushing 108 is provided which snuglyand engagingly fits within enlarged forward portion or passageway 36' ofbore or hollow 34 within anchor housing 20. Cement extruder 10-8 fitsclosely and snugly about tendon 12 passing therethrough such as toprevent grout or cement from entering anchor assembly 100 at thisforward end portion thereof.

Recess or pocket former 102 is hollow and preferably formed from afrangible material of good release properties, such as a suitableplastic. Cavity forming spacer 102 includes an outer conical shapedshell portion 110 and an inner centrally disposed, hollow cylinderportion 112, through which tendon 12 passes and which is connected tothe outer conical shell portion 110I by suitable webs such as 114 and116. Webs 114 and 16 are joined or connected at 11S adjacent their outerends to seal pocket former 10-2. Additional webs, such as indicated bydotted lines at 119 and 120, may join outer -shell 110 and innercylinder 112 to further strengthen and rigidify pocket or recess former102. The rearward end of inner cylinder portion 112 of recess former 102stops short of the formwork or shuttering 118, while the rearward edgeof outer shell portion 110 of pocket former 102 extends completely tothe formwork 18 to form a seal therewith when the parts of the assemblyare tightened together. The inner end 122 of outer shell 110 extendsoutward beyond anchor 20 :and forward of rearward end portion 35'thereof to form an effective seal with anchor housing 20 to preventcement from entering the anchorage assembly at this point. The forwardend portion 123 of central hollow cylinder portion 11'2 of recess former102 is enlarged to generally accommodate and conform to Vthe shape ofbayonet fitting or member 104.

Bayonet fitting 104, which is releasable and detachable includes acircular elongated hollow portion 124 having a threaded outer endportion 126 and an enlarged c ircular forward end portion 12,8 connectedto elongatedV portion 124 by a transition portion 130. Elongated portion124 is positionable through the opening of hollow cylinder 112 of recessformer 102 and through opening or passageway 30 within formwork 18'.IEnlarged forward end portion 128 of bayonet fitting' 104 ispositionable within enlarged rearward portion or cavity 40 of anchorhousing 20', and a pair of flanges or shoulders 132 and` 134 on forwardend portion 128 of bayonet 104 are 'respectively engageable behind andwith lips or shoulders 92 and 94 of anchor housing 20. Bayonet fittingor member 104 has a portion removed therefrom to form a slot or opening136 extending over yits entire length such that fitting 104 can beslipped transversely over or` clipped on cable or strand 12, therebyeliminating the need ofthreading fitting 104 over the entire length ofstrandZ upto' the pointwhere itv is desired to be put to use.Additionally bayonet or hollo'w member 104` is provided with'fav"V-notchw138i' extending about its entire cirduiriferenc and positioned'on enlarged forward end portion `128 adjacent transition'po'rtion 130.V-notch 138 permits 'iittin'g 104 'to be broken "oi 'at'this point, suchas when iormworlt' 1,8 is stripped away from the hardned concrete,leaving'only the enlarged forward end por-k tion 128 with anges orshoulders'132 and 134 of bayonet 1041`n anchor housing`40'.""Alternatively fitting 104 instedofr-being'brokenoff by V-notch138 can be removed from anchor 20' by simple rotation of and release ofanges 132 and 134 from behind lips or shoulders 92 and 94 and reusedwith another casing, similar to casing 20', at another point alongtendon 12.

In like manner nut 106v has a portion or section removed or cut-out fromits entire thickness to provide a slot or opening 140 therealong wherebythe nut may be transversely slipped over or clipped on strand 12 toeliminate threading of the nut over the entire length of strand 12 up tothe point where it is intended to be used.

The embodiment of strand anchor assembly 100` depicted in FIGS. 8through l1 has particular applicability when employed along themid-portions or sections of a particularly long strand which is to beused in the stressing of concrete. When thus employed, using the readilyslottable recess former 102, slotted bayonet fitting 104 and slotted nut106, the assembly can be readily arranged and assembled on themid-portion of the strand or tendon without the necessity of threadingthese por- Vtions or parts of assembly 100 over the entire length of thestrand from its end to its mid-portion. In this use pocket or recessformer 102 is split at reference number 115 where webs 114 and 116y arejoined together and then placed or clipped over strand 12. Next the slotso formed in recess former 102 is closed by joining webs 114 and 116together with staples 117 or the like. Now yslotted bayonet fitting 104is clipped over strand 12 and located and secured in cavity 40 of anchor20'. The pocket former 102 is then pushed over fitting 104 and the wholeassembly 100 is lined up in slot or opening 30in formwork 18, afterwhich split nut 106 is clipped on strand 1-2 and tightened on threadedportion 126` of tting 102 against the outer face of formwork 18-adjacent opening 30 therein. When anchorage assembly 100 is used in themid-portions of an extended tendon, anchor 20' is usually placed on thestrand in the factory at the approximate position at which it will beused before the strand is shipped to the location for use. Once theconcrete has set and cured, formwork 18 is stripped by means of leveragebetween the formwork and the concrete, thus breaking of bayonet tting104 at notch 1358. Pocket former 102 is then extracted to leave anchorhousing and lenlarged forward end portion 128 of bayonet fitting 104recessed within the concrete.

While only certain preferred embodiments of this invention have beenshown and described by way of illustration, many modifications Ywilloccur to those skilled in the artand it is, therefore, desired that itbe understood that it is;l intended in the appended claims to cover allsuch modifications as fall within 'the true spirit and scope ofthisinvention.` l y, f

What is claimed as new and 4what it is desired to secure by LettersPatent ofthe UnitedStates is:

1.` A method for forming a stressed concrete structure including apost-stressing tendon, extending between a pair of opposed and spacedformwork members and fixed with respect to one of theformwork membersand a tendon.

anchorage positioned inwardly of the` other formwork member with thetendon passing through the other form'- work member and anchoragecomprising the steps of securing a means including a temporary andpositive locking means anda void forming means surrounding thelocking-means to the anchorage with the locking means 8 extending fromthe anchorage andv passing'` ai in the concrete when it is setandthrough thefother lfornir- Work member at a predetermined spacedposition there'- fr'om, urging the anchorage toward the other trmworl'gmember with the void `forming means sandwichedbetwee'n the anchorage andthe other formwork'membe'b'y adjus't able means attached'to the lockingmeans outwardly/pf and bearingly against the other form'work m mbert'ro.tix the anchorage in proper positionwith respectto the other formworkmember and the tendon andto tight sealthe void forming means totheanchorage and the o lr formwork member, pouring the concrete `withinetheformworli members and about the tendon and Athe.anc'ihorage and aboutthe void forming means, completely removing the void forming means andlocking means after the concrete has set, stressing the tendon, andsetting the anchorage to grip and retain the tendon under tension. p f i2. In the method as deiined in claim 1 wherein said void forming meanscomprises a spacer member separate from said locking means, said step ofsecuring a-means including the step of inserting the spacer membertightly sandwiched between the anchorage and the other formwork memberwith the spacer member eXtendingabout-the locking means to form the voidin the set concrete.

3. In the method as deiined in claim 1 further comprising the step oftemporarily setting the anchorage .to grip the tendon prior to said stepof pouring the concrete. ,v

4. The method as defined in claim 3 wherein said void forming meanscomprises a spacer member separate-,from said locking means, said stepof securing a means ,includ-` ing the step of inserting the spacermemberbetweenthe anchorage and the other formwork member Awith thespacer member extending about the locking means to form the void in theset concrete. t

5. A method for forming a stressed concrete` structure including apost-stressing tendon extending between a pain of opposed and spacedformwork members and fixed with respect to one of the formwork members*and a tendon anchorage positioned inwardly of 'the other formworlemember with the tendon passing through the other form-r- Work member andanchorage comprisingthe steps offsecuring a means including a temporaryand positive locking means and a void forming means to the anchoragewith the locking means passing throughthe other form# work member at apredetermined spaced Vpositirnrlthere= from, removably fastening thelocking means'externally of and bearingly against the other formworkmember with: the anchorage urged toward the other formwork member andwith the void forming means sandwiched therebetween in sealing relationto the anchorage and thefother formwork member, pouring the concretewithin the formwork members and about the tendon and the anchorageandthe' void forming means, removing the void forming' means and lockingmeans after the concrete has set, stressing the tendon, and setting theanchorage to grip -lan'dretainI the tendon under tension. :r i 1 f,-

6. In the method as defined in claim 5 wherein-'said' locking meansincludes an elongatedmember; and saidi void forming means comprisesa-spacer membenwsaid lstep".

of securing a means including the step of insertingthe'v spacer membertightly sandwiched between the-anchorage. and the other formwork memberwith the jspacerimember extending about the elongated-member to form thevoid. in the set concrete. l

7. In the method as defined in claim S further compris- 9. A methodfor'forming a stressed concrete structure,

the steps prior to pouring the concrete of laying the poststressingcable in place, placing an anchorage means having an aperture about thecable inwardly of the formwork, placing a means for locking and forminga void about the cable with a portion extending through an opening inthe ormwork, temporarily and positively connecting the portion to theanchorage means temporarily and positively securing the portionexternally of the formwork, adjustably urging the portion externally ofthe forrnwork and the attached anchorage means toward the formworkthereby to hold in xed position the anchorage means by the formworkthrough the portion, sealing the portion by another void forming portionsurrounding same between the anchorage means and formwork for preventingthe seepage of concrete therebetween and to form a void in the setconcrete whereby the portion may be removed.

10. In the method as dened in claim 9 wherein the portion comprises asleeve and the void forming portion comprises a spacer, placing thespacer around the sleeve and between the anchorage means and theformwork to prevent seepage of concrete onto the sleeve and to form avoid in the concrete after setting thereof whereby the spacer and sleevemay be removed after setting of the concrete and removal of theformwork.

References Cited UNITED STATES PATENTS 2,781,658 2/1957 Dobell 264-2282,695,754 11/1954 Karig 264-228 2,029,147 1/ 1936 Anderson 249-2173,184,219 5/1965 Simms 254-29 A ROBERT F. WHITE, Primary Examiner T. P.PAVELKO, Assistant Examiner U.S. Cl. X.R.

